It would have to be the variable
The palms of the hands are assumed to be facing forward; arms are at the side.
Out of the following given choices
A. acids B. nutrients C. roots D. soil?
The answer A. Lichens and Moses
secrete organic acids. An example of a secreted
organic acid is oxalic acid. These acids react with mineral in the rocks hence dissolving them. Their decaying vegetation (humus)
also produces acids that weather the rocks. Another way these plants
break rocks are physically using their roots that grow in the cracks and grow bigger.